#ifndef __MY__BUFFER__
#define __MY__BUFFER__
#include "util.hpp"
#include <vector>
#include<assert.h>
namespace zylog{
    #define DEFAULT_BUFFER_SIZE (1*1024*1024)
    #define THRESHOLD_BUFFER_SIZE (8*1024*1024)
    #define INCREMENT_BUFFER_SIZE (1*1024*1024)
    class Buffer{
        public:
            Buffer():_buffer(DEFAULT_BUFFER_SIZE),_writer_idx(0),_reader_idx(0){}
            //向缓冲区写入数据
            void push(const char*data,size_t len){
                //缓冲区剩余空间不够:扩容
                ensureEnoughSize(len);
                //1.将数据拷贝进缓冲区
                std::copy(data, data + len,&_buffer[_writer_idx]);
                //2.将当前写入位置向后偏移
                moveWriter(len);
            }
            //返回可读数据的起始地址
            const char*begin(){
                return &_buffer[_reader_idx];
            }
            //返回可读数据的长度
            size_t readAbleSize(){
                return(_writer_idx-_reader_idx);
            }
            //剩余可写空间大小
            size_t writeAbleSize(){
                return(_buffer.size()-_writer_idx);
            }
            void moveReader(size_t len){
                assert(len<= readAbleSize());
                _reader_idx += len;
            }
            //重置读写位置
            void reset(){
                _writer_idx =0;//缓冲区所有空间都是空闲的
                _reader_idx=0;
            }
            //对Buffer实现交换操作
            void swap(Buffer&buffer){
                _buffer.swap(buffer._buffer);
                std::swap(_reader_idx, buffer._reader_idx);
                std::swap(_writer_idx, buffer._writer_idx);
            }
            //判断缓冲区是否为空
            bool empty(){
                return(_reader_idx==_writer_idx);
            }
        private:
        //对空间进行扩容
            void ensureEnoughSize(size_t len){
                if(len<= writeAbleSize())return ;//不需要扩容
                size_t new_size = 0;
                if(_buffer.size()< THRESHOLD_BUFFER_SIZE){
                new_size =_buffer.size()*2 +len;//小于阈值则翻倍增长
                }
                else {
                new_size =_buffer.size()+ INCREMENT_BUFFER_SIZE + len;//否则线性增长
                }
                _buffer.resize(new_size);
            }
               //对读写指针进行向后偏移操作
            void moveWriter(size_t len){
                assert((len+_writer_idx)<=_buffer.size());
                _writer_idx+=len;
            }
        private:
            std::vector<char> _buffer;
            size_t _reader_idx;//下标，用于标明可读数据的指针
            size_t _writer_idx;//下标，用于标明可写数据的指针
    };
}
#endif